1. Field of the Invention
The invention relates to a linear actuator including an electric motor, a gear housing, a transmission including a planetary gear having a sun wheel, a planetary wheel holder with planetary wheels in mesh with the sun wheel, a toothed rim in the gear housing where the planetary wheels are in mesh with the toothed rim, a spindle in connection with the transmission, a spindle nut on the spindle, and a bearing for embedding an end of a shaft of the spindle.
2. The Prior Art
Linear actuators are well-known components for use in machines and control devices just as they are widely used within the hospital and care sectors, where they are used for adjustable furniture such as beds as well as being used in furniture in general. Another use is adjustable tables, where linear actuators are part of the construction of lifting columns. In all the applications mentioned above, the linear actuator transfers a force between the attachment points in the actuator, typically a rear and front mounting, respectively connected to the rear of the cabinet and the spindle nut, respectively, either constructed directly in the spindle nut or in the front of a tubular activation element connected to the spindle nut.
The construction of linear actuators, which can transfer the forces between the two attachment points without overloading the transmission and thus causing wearing, is difficult and often results in the construction being complicated and voluminous. This is particularly the case where the linear actuator is equipped with a transmission, which comprises a planetary gear.
WO 98/30816 to Linak A/S discloses a linear actuator where the transmission comprises a planetary gear. The solution is as far as it goes fine in that precautions are taken, which leads the axial forces from the spindle around the transmission to the rear mounting. This is realized in that the actuator is equipped with a special metal frame, in which the bearing for the spindle is placed in front of the transmission, and where the frame is connected to the rear mounting by metal rods. The metal rods are lead around the transmission and surround this. Moreover, the spindle is connected to the transmission with a claw clutch, by means of which the transmission is freely suspended and thus is not exposed to axial forces in connection with when the actuator carries a load. As it appears, the construction solves the problem, but in a complicated manner, which is difficult to manufacture as it contains many components. Many components mean more expenses for material and production. Moreover, the structure with the frame surrounding the transmission means that the linear actuator becomes voluminous, which is not desirable, as a compact linear actuator is easier to integrate in an application and easier to handle.
The purpose of the invention is to provide a solution to the outlined problem, i.e. to achieve a more compact linear actuator, which moreover is very simple in its construction, but still is capable of leading the axial forces in the actuator around the transmission.